Hollow metal doors are among the most widely-used types of doors, and find use in virtually all environments in which doors are utilized. In addition to providing a physical access barrier between two areas, it is often desirable for such doors to act as a barrier to the passage of sound, the transmission of heat, and/or the travel of ballistics. Currently-available hollow metal doors have various constructions for providing desired acoustic, thermal, and ballistic performance characteristics. In certain doors, these constructions are provided in the hollow interiors of the door. For example, the hollow interiors of such doors may have mounted therein pads that absorb vibrations to reduce the transmission of sound or metal reinforcements that brace the panels against the impact of ballistics (e.g., windborne debris in severe weather conditions), or the hollow interiors may be filled with an insulating material that reduces the transmission of heat. In other doors, the constructs intended to provide the door with the desired characteristics are mounted to the exposed exterior of the door. However, each of these approaches has certain drawbacks or limitations, such that there remains a need for further improvements in this technological field.